Positive electrode materials for lithium ion batteries and process for preparing the same

Abstract

Provided are a positive electrode material for lithium ion batteries and a process for preparing the same. The positive electrode material for lithium ion batteries comprises a composite positive electrode material consists of LiCoO 2 and an auxiliary positive electrode material, the general formula of the auxiliary positive electrode material is LiCo 1-x-y Ni x Mn y O 2 , wherein 0<x<0.9, 0<y<0.9, 0<x+y<0.9, and the LiCoO 2 is a modified LiCoO 2 coated with an Al 2 O 3 film. The overcharge performance of the batteries can be significantly increased and the use amount of the overcharge additive can be reduced by using the positive electrode material so as to its improve the cycle performance of the batteries and improve the anti-overcharge safety in the special applications and the charging conditions.

What is claimed is: 
     
       1. A positive electrode material for lithium ion batteries, comprising a composite positive electrode material consisting of a modified LiCoO 2  coated with an Al 2 O 3  film and an auxiliary positive electrode material,
 wherein the general formula of the auxiliary positive electrode material is LiCo 1-x-y Ni x Mn y O 2 , 
 wherein 0<x<0.9, 0<y<0.9, 0<x+y<0.9, and 
 wherein the thickness of the Al 2 O 3  film is 0.3-0.4 μm. 
 
     
     
       2. The positive electrode material for lithium ion batteries of  claim 1 , wherein the auxiliary positive electrode material LiCo 1-x-y Ni x Mn y O 2  is present at 10-40% by weight of the composite positive electrode material. 
     
     
       3. The positive electrode material for lithium ion batteries of  claim 2 , wherein the auxiliary positive electrode material LiCo 1-x-y Ni x Mn y O 2  is present at 20-30% by weight of the composite positive electrode material. 
     
     
       4. The positive electrode material for lithium ion batteries of  claim 1 , wherein the median diameter of the LiCoO 2 , without the Al 2 O 3  film, is 9-20 μm. 
     
     
       5. The positive electrode material for lithium ion batteries of  claim 4 , wherein the median diameter of the LiCoO 2 , without the Al 2 O 3  film, is 12-15 μm. 
     
     
       6. The positive electrode material for lithium ion batteries of  claim 1 , wherein the median diameter of primary particles of the auxiliary positive electrode material LiCo 1-x-y Ni x Mn y O 2  is 0.5-5 μm. 
     
     
       7. The positive electrode material for lithium ion batteries of  claim 6 , wherein the median diameter of primary particles of the auxiliary positive electrode material LiCo 1-x-y Ni x Mn y O 2  is 2-3.5 μm. 
     
     
       8. The positive electrode material for lithium ion batteries of  claim 1 , wherein
 the median diameter of the LiCoO 2 , without the Al 2 O 3  film, is 9-20 μm, and 
 the median diameter of primary particles of the auxiliary positive electrode material LiCo 1-x-y Ni x Mn y O 2  is 0.5-5 μm. 
 
     
     
       9. The positive electrode material for lithium ion batteries of  claim 8 , wherein
 the median diameter of secondary particles of the auxiliary positive electrode material LiCo 1-x-y Ni x Mn y O 2  is greater than the median diameter of primary particles of the auxiliary positive electrode material LiCo 1-x-y Ni x Mn y O 2 , and is 5-20 μm. 
 
     
     
       10. The positive electrode material for lithium ion batteries of  claim 1 , wherein
 the median diameter of the LiCoO 2 , without the Al 2 O 3  film, is 12-15 μm, 
 the median diameter of primary particles of the auxiliary positive electrode material LiCo 1-x-y Ni x Mn y O 2  is 2-3.5 μm, and 
 the median diameter of secondary particles of the auxiliary positive electrode material LiCo 1-x-y Ni x Mn y O 2  is greater than the median diameter of primary particles of the auxiliary positive electrode material LiCo 1-x-y Ni x Mn y O 2 , and is 10-15 μm. 
 
     
     
       11. A lithium ion battery comprising electrode pieces of positive electrode,
 wherein a material of the electrode pieces of positive electrode comprises a composite positive electrode material consisting of a modified LiCoO 2  coated with an Al 2 O 3  film and an auxiliary positive electrode material, the general formula of the auxiliary positive electrode material is LiCo 1-x-y Ni x Mn y O 2 , 
 wherein 0<x<0.9, 0<y<0.9, 0<x+y<0.9, and 
 wherein the thickness of the Al 2 O 3  film is 0.3-0.4 μm. 
 
     
     
       12. A process for preparing a positive electrode of lithium ion batteries, comprising:
 mixing a conductive agent, a binder and a solvent; 
 mixing a composite positive electrode material consisting of an auxiliary positive electrode material and a modified LiCoO 2  coated with an Al 2 O 3  film and a solvent, the general formula of the auxiliary positive electrode material is LiCo 1-x-y Ni x Mn y O 2 ,
 wherein 0<x<0.9, 0<y<0.9, 0<x+y<0.9, and 
 wherein the thickness of the Al 2 O 3  film is 0.3-0.4 μm; and 
 
 mixing the mixtures as obtained in the above two steps. 
 
     
     
       13. The process for preparing a positive electrode of lithium ion batteries of  claim 12 , wherein the auxiliary positive electrode material LiCo 1-x-y Ni x Mn y O 2  is present at 10-40% by weight of the composite positive electrode material. 
     
     
       14. The process for preparing a positive electrode of lithium ion batteries of  claim 13 , wherein the auxiliary positive electrode material LiCo 1-x-y Ni x Mn y O 2  is present at 20-30% by weight of the composite positive electrode material. 
     
     
       15. The process for preparing a positive electrode of lithium ion batteries of  claim 12 , wherein the step of mixing the mixtures as obtained in the above two steps comprises:
 a first mixing step of mixing and stirring the two obtained mixtures; and 
 a second mixing step of adding a solvent to the stirred mixture and continuously stirring until homogeneous. 
 
     
     
       16. The process for preparing a positive electrode of lithium ion batteries of  claim 15 , wherein in the first mixing step, the stirring speed is 100-300 r/min and the stirring time is 3 min to 1 h; and in the second mixing step, the stirring speed is 2000-5000 r/min and the stirring time is 2-5 h. 
     
     
       17. The process for preparing a positive electrode of lithium ion batteries of  claim 16 , wherein in the step of mixing a conductive agent, a binder and a solvent, the amount of the added solvent is 60% by weight of the total solvents; in the step of mixing a composite positive electrode material and a solvent, the amount of the added solvent is 20% by weight of the total solvents; and in the second mixing step, the amount of the added solvent is 20% by weight of the total solvents. 
     
     
       18. The process for preparing a positive electrode of lithium ion batteries of  claim 12 , wherein the conductive agent is SP, the binder is PVDF and the solvent is NMP.